Microvascular response during skeletal muscle contraction of rabbit hindlimb

Abstract

Effects of light and tetanic muscle contraction on venous out-flow, hematocrit (Hct), plasma total protein (protein), H^+, Pco_2, Po_2 and plasma osmolality through muscle were investigated in the rabbit hindlimb. Metarteriolar vasodilatation and capillary-tissue fluid movement were discussed hydrodynamically. The results obtained were as follow. The degree of contraction hyperemia depended upon the intensity of sciatic nerve stimulation. In light contraction of 1 to 10 Hz the flow increased rapidly from the begining of start. In tetanic contraction of 20 to 50 Hz the flow decreased at the first 15 sec, then increased gradually to the maximal level. In both patterns of contraction hyperemia the rapid increase in Hct and protein were observed. Hct increase on the average was about 104% by 5 Hz and 108% by 50 Hz. Hct_<max> in typical example was about 120% by severe contraction (Hct value : 42.5→51.0%). The percent change in plasma volume calculated from the Hct ratio and proportionality factor was -7.8% by 5Hz and -12.7% by 50Hz. Average protein increase was about 109% by 5 Hz and 116% by 50Hz. The computed increase in protein was approximately +1.2% and +3.3%, respectively. Plasma H^+, Pco_2 and plasma osmolality increased gradually during contraction, and osmolality max was obtained in the first 1&acd;2 min of post-contraction hyperemia. Po_2 decreased gradually during contraction and Po_2 minimal was obtained in a min after contraction. Then, Po_2 retuned to the control level with a slow oscilating changes. The data suggest that the water supply to the tissue may start at the early stage of contraction in a slow blood flow component (true capillaries). Tissue fluid dynamics during contraction was discussed theoretically in connection with the activity of a fast blood flow component (metarteriolar dilatation), pressure difference in arteriole and venule, osmolality in plasma and interstitial fluid and a participation of lymphatics.